Solutions have been proposed for assemblies that allow extended operation of a vehicle after a partial or total loss of air pressure. Many of these systems include multiple components that are complicated and time consuming to use or assemble. U.S. Pat. No. 5,891,279, which is incorporated herein in its entirety by reference, overcomes some of these difficulties. Such patent describes an assembly that includes a tire, a rim with a unique profile designed to accept the tire, and a deformable, but preferably circumferentially inextensible, run-flat support ring that is mounted over an essentially cylindrical bearing surface of the rim. The base of the support ring includes essentially inextensible, circumferentially oriented reinforcement elements to create an interference fit between the support and bearing surface of the rim. U.S. Patent Application Publication US2003/0005991, which is also incorporated herein in its entirety by reference, also describes a rim and run-flat support ring that includes a plurality of zones having protuberances on the bearing surface of the support but without a complementary depression in the rim.
The design of a run-flat support ring includes competing considerations of performance under run-flat conditions and assembly of the run-flat system. A certain amount of axial locating force is required when a run-flat support is mounted upon the rim. Preferably, this force is sufficiently low to allow proper seating of the support during mounting or dismounting. However, for run-flat operation, the force for unseating the ring from the rim must be sufficiently high so that the support maintains its proper position during reasonable vehicle operation. A run-flat support that optimizes these competing considerations while also providing improved handling characteristics during run-flat operation is preferred.
Furthermore, even when manufactured within reasonable and acceptable tolerances, a run-flat support having a diameter that is within the low end of its manufacturing tolerance may be particularly difficult to mount and dismount with a rim having a diameter that is within the upper end of its manufacturing tolerance. A run-flat support that more readily tolerates variances of the support and rim within the allowed manufacturing tolerances is also preferred.